Researchers from Helwan University (Cairo, Egypt) developed a system to extract water from humid air. The system uses calcium chloride (a desiccant) to capture the water vapors; then the water is released from the desiccant using the sun energy, and collected in a tank, with practically no running costs. This innovative system can be used to obtain water in remote areas.
Water shortage is a major problem which affects much of the world, especially (but not only) remote areas in less developed countries. Water shortages are due to both natural causes such as droughts, and human activities such as pollution of water sources, and poor management.
This problem has serious consequences; some people, for instance, do not have access to drinkable water and can therefore contract diseases. Moreover, activities such agriculture/farming are also heavily affected; this, in turn, can have an effect on the economy and well being of the society.
Addressing the Problem
To try to solve this problem, scientists and engineers have been developing techniques to make the most of the water available.
Treating and purifying polluted waters, for instance, means that the water can be reused either for drinking or for agriculture. Desalination of sea waters is another methodology which can give fresh/drinkable waters; the process, however, is quite expensive as it requires lot of energy.
Water from the Air
Drinking water can also be obtained by extracting it from humid air. This idea is very interesting and promising; it could be an excellent solution to have fresh water from a renewable source, especially for remote and decentralized areas.
A way to do extract water from the air is to cool it to a temperature low enough for the water to condense (dew point) and then collect the liquid formed.
Alternatively, it is possible to collect water using appropriate desiccant materials which adsorb the water vapors on their surfaces. These materials are subsequently heated, so the water can be removed and collected.
The main drawback of both methods, however, is that they may need relatively high amounts of energy, as either cooling the air or heating up the desiccant materials are both processes which require much energy.
Innovative System for Water Extraction
Scientists have been trying to improve/optimize the process to extract water from air, to make it more efficient and energy sustainable.
Researchers from the Faculty of Engineering El Mattaria of Helwan University (Cairo, Egypt) developed an innovative system, which uses solar energy for the water extraction. They published their results in Energy in July 2015.
Decoded Science spoke to Dr. George Elia William, one of the scientists involved in the study; he explains the details and the meaning of their study.
“To make water extraction feasible and more sustainable, we decided to “take advantage” of the differences in temperature between day and night time.
The idea is that at night time the weather is cold, so water vapor can be adsorbed by the desiccant material; during the day, the desiccant is exposed to the heat coming from the sun, so the water is removed from absorber. The water can be then collected and the desiccant material will be dried, so it can be used again. In this way we do not need any energy source for the process to run.”
To do this, Dr. William and his coworkers used a test rig (see the picture on the side) with a specific geometry and made with appropriate materials.
The rig has a trapezoidal shape with four sides, which are all covered with transparent fiber glass panels. Inside, it has several shelves, which hold the desiccant material.
“As desiccant, we used calcium chloride (CaCl2), a common and cheap hygroscopic salt. We spread it on two different kinds of “host” substrates, either dark cloth or sand.
During the night, the system is open to contact with air; hence the desiccant captures the water vapor. During the day, the system is closed but the sun energy can still go through, as the fiber glass is transparent. In this way, the water evaporates from the desiccant; when in contact with the fiber glass panels, it condenses, due to difference in temperature. The condensed water is then collected in a tank at the bottom.”
Monitoring the Water Collection
Dr. William and his coworkers performed a series of experiments with this rig.
“We saw that many different parameters may affect the efficiency of the system, i.e. the water collected. We could not control some of these parameters, like the weather conditions, while we could control others, i.e. the desiccant concentration, the number of shelves, etc.
Regarding the weather, we monitored the rig during the summer months in Cairo (Egypt); we saw that both day and night time temperatures had an effect on water collection. Other parameters such as air humidity and wind speed were also crucial.”
Overall, Dr. William and coworkers were able to collect in a day up to 2.3 liters of water per m2 of incident solar radiation. That’s less than 11 square feet of rig to collect over half a gallon of water, in just one day, with no energy cost.
“Our rig costs only about 100 $ to assemble and it has practically no running costs. Considering this, the results we obtained are really encouraging.
We will continue working on the system to make it even more efficient; key steps to improve it will be to employ new desiccant materials which can capture more water and have lower regeneration temperature.”
Towards More Sustainable Water from Air Extraction
Water shortages are likely to be an even more serious problem in upcoming years; because of this, it is essential to recover water from all possible sources.
The development of sustainable systems to extract water from humid air is surely one of the ways to do this, since fresh water in the atmosphere represents a massive and renewable source. Rigs like those developed in this study can be particularly beneficial for small and remote communities, not easily reachable by other means.
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